CHILLED BEAMS & F FANSAN COILS


achieve the required comfort conditions. ISO7730 states a DR of <20% is necessary for a CAT B environment.


Solutions for both cooling and heating There are a number of diff users that Trox has designed


specifi cally for applications where a suspended ceiling is absent. The Trox Tellus swirl diff user is one option. It works diff erently to most diff users on the market, as it has a gap between the diff user face and the plenum which allows for the air to discharge horizontally and form a ‘Coanda jet’. The air fl owing through the swirl pattern face connects to this jet, increasing the throw distance. For high rooms, Tellus can be provided with a centre punched face for vertical air discharge. Another option is the Trox RFD swirl diff user. This has an increased diameter discharge nozzle (Dx Face), which ensures the diff user works well in an exposed application without requiring the high discharge velocities and pressures. If the system is required to provide heating to the space as well as cooling, there are additional challenges to be overcome. Without a suspended ceiling the warm air is free to stratify. As a result, the space above the diff users will be heated before the occupied zone, wasting energy, slowing the rate temperature change, and possibly creating discomfort (due to high temperature gradients between head and ankle).


The answer to this, and other problems, is the use of variable geometry diff users. The new Trox RFD-V, for example, is designed with a thermal actuator and an internal mechanism to manage air more eff ectively. An adjustable internal sleeve enables the unit to move between horizontal and vertical air discharge, depending on whether the system needs to cool or warm the space. During cooling the air discharge is horizontal and radial. As the supply temperature increases the discharge pattern will switch automatically to vertical, directing warmer air more eff ectively into the occupied space. Once the supply temperature decreases, the air discharge switches back to horizontal once more. These changes to air discharge are controlled by an integral thermal actuator, within the diff user which, in turn, controls the internal sleeve. The supply air to room air


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temperature diff erence may range from -10 to +15K. By facilitating the ability to move automatically between cooling and heating, a variable geometry diff user enables the comfort conditions for the occupied space to be managed much more eff ectively.


Acoustic issues Exposed ceilings are also associated with acoustic


unpredictability. Without the normal sub-division of zones between the works of a room and the occupants of a room, a poorly thought through design can create large amounts of reverberating noise. Suspended ceilings are typically constructed from metal tiles which incorporate acoustic materials that absorb sound, minimising noise and reducing the reverberation time within the occupied space. Without these materials in the vicinity of building services, especially in former industrial environments with hard walls, ambient noise stays around and creates an exponential problem for occupants. Removal of a suspended ceiling can, therefore, cause the noise level of HVAC to increase. For an FCU, this eff ect can lead to around an 8NR increase to the noise level. As well as fan coil units, the acoustic eff ects of other HVAC elements, normally installed behind a false ceiling, need to be considered. Such as common extracts (e.g. bell mouths), CAV/VAV and any equipment further upstream that now has a direct sound path to occupants (AHUs). To assess the acoustic requirements for a room with


exposed services, a direct noise contribution therefore needs to be calculated. This includes assessment for: ■% leaving outlet ■Distance to listener ■Directivity ■Reverberation time. With the correct selection and placement of equipment, together with the intelligent use of silencers etc, the problem can be mitigated, but the key is appreciating acoustics carefully within the assessment phase. To conclude, careful selection of equipment designed


with exposed ceiling applications in mind can provide the required comfort conditions, whilst enabling architects and interior designers to achieve their aesthetic ambitions.


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Standard ceiling diff users are only designed to work with an adjacent ceiling surface. If the ceiling system is removed, for an exposed ceiling, almost all standard diff users will be unable to function correctly.


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